The acronym “KVM” stands for Keyboard, Video and Mouse. This represents a class of switching systems designed to provide user(s) centralized control and monitoring of multiple computers (“host computers”) from a single keyboard, monitor and mouse (“operator control center” or “OCC”). The OCC may be located remotely from the host computers. A KVM system works by allowing the user to select a host computer to monitor and control from the OCC. The user may select the host from an interface displayed on the OCC monitor (the “On Screen Display” or “OSD”) or from controls located on the front panel of the KVM unit. The KVM system switches the video signals of the selected host computer to the OCC monitor so that the user may view the host video from the OCC. The KVM system also routes or “switches” the Keyboard and Mouse signals of the OCC to the respective ports of the selected host computer. From the host computer's perspective, it appears as if the OCC's keyboard and mouse are directly attached to the host.
Users of KVM systems include system administrators, developers, software or hardware engineers, technicians, graphic artists, etc. Examples of tasks that are commonly performed with KVM systems include monitoring applications that are running on the host computers, installing or upgrading software applications or programs, and re-booting the host computers. KVM systems are commonly used by Internet Service Providers (ISPs). ISPs require a large number of computers or “server farms” to handle the large volume of Internet traffic and data. ISPs use KVM systems to provide centralized oversight over the server farms, thereby reducing the burden of computer maintenance and administration.
KVM systems are also used in distributed processing where applications are run using the processing power of a number of interconnected computers. For example, it is becoming increasingly popular to use computer generated images for animation and special effects in movies. Computer graphics of this kind entail a large amount of intensive calculations and often require more processing power than is available from any one computer standing alone. In order to enhance processing power and speed, tasks are distributed over a number of host computers. KVM systems allow for control and monitoring of these computers from a single OCC.
The benefits provided by KVM systems include the time saved by eliminating the need to travel from host to host to monitor or operate each host computer. In addition, the keyboards, monitors and mice of the host computers are no longer needed and can be eliminated, thereby saving money and space.
The performance demands of a KVM system for switching video data has increased with the increase in monitor resolution. The higher the monitor resolution, the higher the processing speed required by the KVM system to deliver the video signals to the OCC display without degradation. The approximate speed required by a KVM video switch for a given resolution can be estimated as follows: ((number of horizontal pixels)×(number of vertical pixel lines)×(85 Hz refresh rate of 85 images per second))×(1.45 factor to allow time for vertical and horizontal retrace). Conventional KVM systems, operating at speeds of 250 MHz or less, are sufficient to accommodate many but not all standard monitor resolutions. Those resolutions that may be accommodated by conventional KVM systems include VGA (640 ×480 pixels), SVGA (800×600 pixels), XGA (1,024×768 pixels), and SXGA (1,280×1,024 pixels). For example, SXGA requires a processing speed of approximately (1,280×1,024)×85 Hz×1.45, which is approximately 162 MHz, and is less than 250 MHz.
Video displays under the QXGA image resolution standard of 2048×1536 pixels (3,143,728 pixels) and higher, however, are required to function at speeds approximating 400 MHz. Using the formula described above, the approximate speed required for the QXGA resolution is 388 MHz, which is (2048×1536)×85 Hz×1.45. Conventional KVM systems, operating at speeds of 250 MHz or less, are therefore unsuitable for higher resolution video.
Conventional KVM systems are limited to speeds of less than 250 MHz for several reasons. One reason is that the circuitry used by conventional KVM systems to implement the video switches is inadequate. The types of video circuitry used by conventional KVM video switches are either Resistor-Transistor Logic (RTL) or Large-Scale Integration (LSI) circuits.
KVM systems using RTL circuitry are comprised of resistors and bipolar transistors. The RTL implementation requires a large number of the resistor and bipolar-transistor components and therefore consuming a large portion of the limited space available on the printed circuit board (PCB) of the KVM unit. The large number of components required for an RTL switch also makes these switches difficult to assemble. For the above reasons, RTL switches are undesirable at the speeds required by higher resolution video standards such as QXGA.
The other type of circuits used in conventional KVM systems are LSI circuits, which are circuits having a large number of electronic components integrated on a single chip. For example, U.S. Pat. No. 5,884,096, Beasley et al., utilizes LSIs. See, e.g., Col. 8, Lines 11-28. LSIs, however, are in extremely limited supply at speeds above 200 to 250 MHz. Implementing a KVM system using LSIs at speeds near 400 MHz would be prohibitively expensive.
Another factor inhibiting the use of high speed video in KVM systems is the problem of video degradation caused by the “roll-off” effect. The roll-off effect refers to a decrease in the amplitude of a signal as the frequency of the signal increases. This effect is caused by the impedance of the conventional connectors, such as DB-25 connectors, through which the analog video signals pass as they travel through the KVM system. The roll-off effect is significant in video applications operating at speeds above 250 MHz and causes attenuation of video signals at the higher operating speeds. To the user, the resulting image appears “soft”, i.e., having non-crisp edges, color aberrations, and generally blurred text characters. Therefore, the roll-off effect poses an additional problem for high speed video KVM systems.
KVM systems may be controlled from a set of controls located on the front panel of the KVM unit, from keyboard sequences or “hot keys”, and/or from an On Screen Display (“OSD”). The OSD is an interface displayed on the monitor of the OCC to allow the user to control the KVM system. The OSD is typically more convenient and offers more features than the other means of control. The OSD may be text based or graphics based. Conventional KVM systems present the OSD to the OCC monitor using summing operational amplifiers to “add” or sum the OSD video data “on top of” the video data originating from the host computer. This creates a transparent effect where the host computer video appears as a background to the characters of the OSD text or banners. For a display having a transparent background, the OSD may be difficult to read if there is insufficient contrast between the OSD characters and the background host computer video. In addition, the transparent effect created by the summing of the OSD video on top of the host video is inconsistent with the look and feel of most modem operating systems, in which windows are typically displayed with an opaque background.